In the manufacture of semiconductor devices, various heat treatment apparatuses are used in order to apply various treatments, such as oxidation, diffusion, CVD, and so forth, to semiconductor wafers, i.e., the target substrates. As one of such heat treatment apparatuses, there is known a type in which a lord-lock chamber, i.e., a preparatory vacuum chamber is connected to a treatment chamber, i.e., a heat treatment furnace. In the case of this heat treatment apparatus, by previously setting the interior of the preparatory vacuum chamber at approximately the same pressure as that in the heat treatment furnace, the wafers can be transferred in and out by opening the furnace throat without restoring the pressure in the heat treatment furnace to the atmospheric pressure; and thus, the reduction of the required time and the improvement in throughput can be realized.
By the way, in the case of the above-mentioned heat treatment apparatus, it is required to execute the maintenance thereof for the periodical inspection of the heat treatment furnace, the washing of the reaction tube, etc. in order to retain its reliability. In the case of a vertical heat treatment apparatus having its furnace opening or throat in the lower portion thereof, it is structurally possible to open for instance the interiors of the heat treatment furnace and the preparatory vacuum chamber to the atmosphere and to lower the reaction tube etc. into the preparatory vacuum chamber located therebeneath, whereby the maintenance thereof is executed.
However, in the heat treatment apparatus, moisture, dust, etc. are apt to enter the interior of the preparatory vacuum chamber since the preparatory vacuum chamber is opened to the atmosphere. Further, there is another problem that a long period of time must be spent for the re-starting for restoring the interior of the preparatory vacuum chamber to a predetermined degree of vacuum. Further, due to the fact that the heat treatment furnace is moved down into the preparatory vacuum chamber, the preparatory vacuum chamber needs to be formed large; and thus, the whole apparatus is increased in size, which is a problem, too.
There has also been proposed a heat treatment apparatus constructed such that a gate valve is interposed between the heat treatment furnace and the preparatory vacuum chamber, so that, by closing this gate valve, the interior of the heat treating chamber and the interior of preparatory vacuum chamber are cut off from each other. In this case, it is possible to execute maintenance by removing the heat treatment furnace, while maintaining the interior of the preparatory vacuum chamber in vacuum state. However, in this heat treatment apparatus, the apparatus is increased in size by an amount corresponding to the gate valve. Further, it is necessary to manufacture the gate valve in accordance with special specifications for a water-cooling structure to protect the gate from thermal influence. Therefore, the apparatus not only becomes structurally complicated, but also there is a problem that the products resulting from the water cooling attach, causing the formation of particles.
Further, also known is a vertical heat treatment apparatus having a lid movable up and down, which opens or closes the furnace throat formed in the lower portion of the heat treatment furnace. On the lid, a quartz-made boat, i.e., a substrate holding member which can hold a plurality of wafers is placed through a quartz-made heat insulation cylinder. The boat and the heat insulation cylinder are inserted into the furnace, whereby heat treatment is applied to the wafers for film formation etc. In such a vertical heat treatment apparatus, films are also formed on the boat and the heat insulation cylinder, so that to perform maintenance works, such as the washing or replacement of the members periodically or when required, becomes necessary.
However, in the case of the above-mentioned vertical heat treatment apparatus, the boat and the heat insulation cylinder must be taken out by opening the preparatory vacuum chamber to the atmosphere, in order to perform the maintenance works for the boat and the heat insulation cylinder. As a result, there arises a problem that, moisture, dust, etc. are apt to enter the preparatory vacuum chamber, which has been opened to the atmosphere, and a considerable period of time must be spent for the re-starting for restoring the interior of the preparatory vacuum chamber to a predetermined degree of vacuum.